Explanation:
so,
y = -9x + 2
now we need to transform this equation that actually x is calculated out of y.
and then, at the end, to make the inverse function a formally correct function, we rename x to y and y to x.
so,
y = -9x + 2
y - 2 = -9x
x = -(y - 2)/9 = (-y + 2)/9
=> for a formal function definition
y = (-x + 2)/9